This invention relates to a means for reducing the cost of electrical energy from photovoltaic cells. These cells are remarkable energy sources having no moving parts and a lifetime of many years when suitably protected. However photovoltaic cells are very expensive. As a result, their applications have been limited to space power systems and to a few special terrestial applications.
The power that a photovoltaic cell can produce is a function of the insolate sunlight and a typical solar cell can utilize efficiently many times the normal solar insolation, provided that the temperature of the solar cell does not increase excessively. Therefore, a solar concentrator can be effective; and within limits, the electrical output of the photovoltaic cell will increase with the concentration factor. At appreciable concentration factors, cooling is required, since the efficiency of photovoltaic cells may decrease rapidly with increasing temperatures. In fact some silicon solar cells become completely ineffective at temperatures below 200.degree. C.
Many types of solar concentrators have been studied including reflective and refractive devices. The large amount of material in refractive devices of conventional design adds to the cost. The precise construction required for solar concentrators and for the tracking mechanism to point the optical system towards the sun and the requirement for cooling systems have made optical concentrators uneconomical for most applications.